GeoMagneticModelLoader.java

  1. /* Copyright 2011-2012 Space Applications Services
  2.  * Licensed to CS Communication & Systèmes (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.models.earth;

  19. import java.io.IOException;
  20. import java.io.InputStream;
  21. import java.io.InputStreamReader;
  22. import java.io.StreamTokenizer;
  23. import java.nio.charset.StandardCharsets;
  24. import java.text.ParseException;
  25. import java.util.Collection;
  26. import java.util.LinkedList;
  27. import java.util.List;

  29. import org.orekit.data.DataLoader;

  31. /** Loads geomagnetic field models from a given input stream. A stream may contain multiple
  32.  * models, the loader reads all available models in consecutive order.
  33.  * <p>
  34.  * The format of the expected model file is either:
  35.  * <ul>
  36.  *   <li>combined format as used by the geomag software, available from the
  37.  *       <a href="http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html">IGRF model site</a>;
  38.  *       supports multiple epochs per file</li>
  39.  *   <li>original format as used by the
  40.  *       <a href="http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml">WMM model site</a>.
  41.  * </ul>
  42.  * <p>
  43.  * <b>Combined Format</b>
  44.  * <pre>
  45.  *     {model name} {epoch} {nMax} {nMaxSec} {nMax3} {validity start} {validity end} {minAlt} {maxAlt} {model name} {line number}
  46.  * {n} {m} {gnm} {hnm} {dgnm} {dhnm} {model name} {line number}
  47.  * </pre>
  48.  * <p>
  49.  * Example:
  50.  * </p>
  51.  * <pre>
  52.  *    WMM2010  2010.00 12 12  0 2010.00 2015.00   -1.0  600.0          WMM2010   0
  53.  * 1  0  -29496.6       0.0      11.6       0.0                        WMM2010   1
  54.  * 1  1   -1586.3    4944.4      16.5     -25.9                        WMM2010   2
  55.  * </pre>
  56.  * <p>
  57.  * <b>Original WMM Format</b>
  58.  * <pre>
  59.  *    {epoch} {model name} {validity start}
  60.  * {n} {m} {gnm} {hnm} {dgnm} {dhnm}
  61.  * </pre>
  62.  * <p>
  63.  * Example:
  64.  * </p>
  65.  * <pre>
  66.  *    2015.0            WMM-2015        12/15/2014
  67.  *  1  0  -29438.5       0.0       10.7        0.0
  68.  *  1  1   -1501.1    4796.2       17.9      -26.8
  69.  * </pre>
  70.  *
  71.  * @author Thomas Neidhart
  72.  */
  73. public class GeoMagneticModelLoader implements DataLoader {

  75.     /** The loaded models. */
  76.     private List<GeoMagneticField> models = new LinkedList<GeoMagneticField>();

  78.     /** Returns a {@link Collection} of the {@link GeoMagneticField} models that
  79.      * have been successfully loaded. The {@link Collection} is in
  80.      * insertion-order, thus it may not be sorted in order of the model epoch.
  81.      * @return a {@link Collection} of {@link GeoMagneticField} models
  82.      */
  83.     public Collection<GeoMagneticField> getModels() {
  84.         return models;
  85.     }

  87.     /** {@inheritDoc} */
  88.     public boolean stillAcceptsData() {
  89.         return models == null || models.isEmpty();
  90.     }

  92.     /** {@inheritDoc} */
  93.     public void loadData(final InputStream input, final String name)
  94.         throws IOException, ParseException {

  96.         // open data file and parse values
  97.         final StreamTokenizer str = new StreamTokenizer(new InputStreamReader(input, StandardCharsets.UTF_8));

  99.         while (true) {
  100.             final GeoMagneticField model = readModel(str);
  101.             if (model != null) {
  102.                 models.add(model);
  103.             } else {
  104.                 break;
  105.             }
  106.         }
  107.     }

  109.     /** Read the model from the given {@link StreamTokenizer}.
  110.      * @param stream the stream to read the model from
  111.      * @return the parsed geomagnetic field model
  112.      * @throws IOException if an I/O error occurs
  113.      */
  114.     private GeoMagneticField readModel(final StreamTokenizer stream) throws IOException {

  116.         // check whether there is another model available in the stream
  117.         final int ttype = stream.nextToken();
  118.         if (ttype == StreamTokenizer.TT_EOF) {
  119.             return null;
  120.         }

  122.         if (ttype == StreamTokenizer.TT_WORD) {
  123.             return readCombinedFormat(stream);
  124.         } else {
  125.             return readOriginalWMMFormat(stream);
  126.         }
  127.     }

  129.     /** Read a magnetic field from combined format.
  130.      * @param stream the stream to read the model from
  131.      * @return magnetic field
  132.      * @throws IOException if some read error occurs
  133.      */
  134.     private GeoMagneticField readCombinedFormat(final StreamTokenizer stream)
  135.         throws IOException {
  136.         final String modelName = stream.sval;
  137.         stream.nextToken();
  138.         final double epoch = stream.nval;
  139.         stream.nextToken();
  140.         final int nMax = (int) stream.nval;
  141.         stream.nextToken();
  142.         final int nMaxSecVar = (int) stream.nval;

  144.         // ignored
  145.         stream.nextToken();

  147.         stream.nextToken();
  148.         final double startYear = stream.nval;

  150.         stream.nextToken();
  151.         final double endYear = stream.nval;

  153.         final GeoMagneticField model = new GeoMagneticField(modelName, epoch, nMax, nMaxSecVar,
  154.                                                             startYear, endYear);

  156.         // the rest is ignored
  157.         stream.nextToken();
  158.         @SuppressWarnings("unused")
  159.         final double altmin = stream.nval;

  161.         stream.nextToken();
  162.         @SuppressWarnings("unused")
  163.         final double altmax = stream.nval;

  165.         stream.nextToken();
  166.         stream.nextToken();

  168.         // loop to get model data from file
  169.         boolean done = false;
  170.         int n;
  171.         int m;

  173.         do {
  174.             stream.nextToken();
  175.             n = (int) stream.nval;
  176.             stream.nextToken();
  177.             m = (int) stream.nval;

  179.             stream.nextToken();
  180.             final double gnm = stream.nval;
  181.             stream.nextToken();
  182.             final double hnm = stream.nval;
  183.             stream.nextToken();
  184.             final double dgnm = stream.nval;
  185.             stream.nextToken();
  186.             final double dhnm = stream.nval;

  188.             model.setMainFieldCoefficients(n, m, gnm, hnm);
  189.             if (n <= nMaxSecVar && m <= nMaxSecVar) {
  190.                 model.setSecularVariationCoefficients(n, m, dgnm, dhnm);
  191.             }

  193.             stream.nextToken();
  194.             stream.nextToken();

  196.             done = n == nMax && m == nMax;
  197.         } while (!done);

  199.         return model;
  200.     }

  202.     /** Read a magnetic field from original WMM files.
  203.      * @param stream the stream to read the model from
  204.      * @return magnetic field
  205.      * @throws IOException if some read error occurs
  206.      */
  207.     private GeoMagneticField readOriginalWMMFormat(final StreamTokenizer stream)
  208.         throws IOException {

  210.         // hard-coded values in original WMM format
  211.         final int nMax = 12;
  212.         final int nMaxSecVar = 12;

  214.         // the validity start is encoded in format MM/dd/yyyy
  215.         // use the slash as whitespace character to get separate tokens
  216.         stream.whitespaceChars('/', '/');

  218.         final double epoch = stream.nval;
  219.         stream.nextToken();
  220.         final String modelName = stream.sval;
  221.         stream.nextToken();
  222.         final double month = stream.nval;
  223.         stream.nextToken();
  224.         final double day = stream.nval;
  225.         stream.nextToken();
  226.         final double year = stream.nval;

  228.         final double startYear = GeoMagneticField.getDecimalYear((int) day, (int) month, (int) year);

  230.         final GeoMagneticField model = new GeoMagneticField(modelName, epoch, nMax, nMaxSecVar,
  231.                                                             startYear, epoch + 5.0);

  233.         // loop to get model data from file
  234.         boolean done = false;
  235.         int n;
  236.         int m;

  238.         do {
  239.             stream.nextToken();
  240.             n = (int) stream.nval;
  241.             stream.nextToken();
  242.             m = (int) stream.nval;

  244.             stream.nextToken();
  245.             final double gnm = stream.nval;
  246.             stream.nextToken();
  247.             final double hnm = stream.nval;
  248.             stream.nextToken();
  249.             final double dgnm = stream.nval;
  250.             stream.nextToken();
  251.             final double dhnm = stream.nval;

  253.             model.setMainFieldCoefficients(n, m, gnm, hnm);
  254.             if (n <= nMaxSecVar && m <= nMaxSecVar) {
  255.                 model.setSecularVariationCoefficients(n, m, dgnm, dhnm);
  256.             }

  258.             done = n == nMax && m == nMax;
  259.         } while (!done);

  261.         // the original format closes with two delimiting lines of '9's
  262.         stream.nextToken();
  263.         stream.nextToken();

  265.         return model;
  266.     }

  268. }
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